I am new to raising chickens. I have 2 roosters and 1 hen (I am not sure of the breed). They are very large white birds with pink legs and feet. They eat and drink very well but are very inactive. In fact, they often lay down to eat and drink. They rarely leave the coop (Actually tractor). They have red bellies and lost all of the feathers on their belly. I have dusted several times for mites using seven dust. the skin on the belly goes from bright red to pink. I also have 9 other hens (much smaller birds and I don't know the breed) that are just fine. No feather loss or red belly. They go outside the tractor everyday. Any help would be appreciated. The Picture below is the hen. The roosters look worse and are much bigger making it difficult to get pictures.